Internal combustion engines include crankcases having a plurality of cylinders. The cylinders contain pistons whose reciprocating motion due to combustion events may be transferred through a crankshaft to yield a torque output of the engine. Often, engine crankcases are made of cast metal, and include features that are either formed or machined therein subsequent to the casting thereof.
Known methods for machining crankcases include the casting of machining datums, or, cast features that are used to locate the casting onto a machining device. By proper placement and location of a casting onto a machining device, positional and tolerance dimensions may be accomplished in the creation of various machined features in a crankcase.
Typical machining datums are “nubs”, or protrusions, that are cast into the metal of the crankcase and that fit into openings in a “table” of a machining device. These nubs typically serve no purpose other than to locate the crankcase, and are usually placed onto surfaces that will eventually be machined themselves thus obliterating the nubs. The reason for deletion of the nubs is primarily to reduce the weight of the finished and machined crankcase, and to also improve the shape, appearance, and fit of same in an engine.
One disadvantage of the existing machining datum configuration, or nubs, for cast metal crankcases is that their shape, typically a rectangular shape, does not allow for alignment of a casting for more than two degrees of freedom of motion. Moreover, existing datum configurations that are obliterated in the finished product do not allow for a dimensional check for the quality of each machining operation in the finished product.
Accordingly, there is a need for an improved machining datum design configuration that allows for location for more than two degrees of freedom of the casting for machining, and that allow for a dimensional check for the quality of each machining operation in the finished product.